Anthropological significance of Tilia trees in Japan

Abstract Tilia (Malvaceae) is a genus of deciduous trees widespread in the northern hemisphere. Tilia species native to Japan include three endemic species, T. japonica, T. maximowicziana, and T. kiusiana, as well as the more widespread T. mandshurica. Other species were also introduced, the most important being T. miqueliana, brought to Japan with the arrival of Buddhism and planted on temple grounds as Bodaiju. Both historically and at present, Tilia trees are valuable to the people in Japan. Some Tilia trees are considered sacred in both Buddhism and Shinto. They are also prominent ornamental and park trees, albeit less popular in Japan than in Europe. Japanese Tilia spp. are used in the manufacturing of honey, cosmetics, lumber (especially plywood and veneers), and traditional bast cloth. Many Tilia trees are significant hubs in pollinator and mycorrhizal networks, but research on Japanese Tilia ecology is scarce. Despite their importance, Japanese Tilia trees have received less scientific attention in comparison with European Tilia species. The most striking example is T. kiusiana, with virtually no scientific literature regarding the species (save for a series of publications studying its secondary metabolites and potential medical uses). Furthermore, most published resources concerning Tilia in Japan are available only in Japanese, restricting their accessibility. This review seeks to translate, collect, and organize the information available on Japanese Tilia species. By doing so, areas are highlighted where new studies are necessary. A better understanding of these important trees would also be instrumental in their conservation.

species, flower color ranges from white to green to yellow. They produce a strong, characteristic smell, are rich in nectar, and are insect-pollinated. The Tilia fruit is round, woody nutlets attached to an elongated bract resembling a small leaf. Tilia can be either di-or tetraploid, a feature important in taxonomic identification (Pigott, 2012).
People have long valued Tilia species for numerous reasons.
They are important honey plants, and humans have been already consuming Tilia honey during the Bronze Age (Kvavadze et al., 2006).
In addition to honey, pharmacologically active compounds can be found in the flowers and leaves of many Tilia species. These compounds have a wide range of effects, including anti-inflammatory, anti-cancerogenic, and antidiabetic (Frezza et al., 2019;Kosakowska et al., 2015;Shimada et al., 2014). Recent studies suggest that Tilia secondary metabolites might also alleviate symptoms of depression (Martínez-Hernández et al., 2021;Turrini et al., 2020).
Another Tilia-derived material that has been used throughout history is bast-fibers obtained from tree bark (Böhlmann, 1971). In regions across North America, Europe, and Asia, Tilia bast was used to make ropes, textiles, and clothes (Oeggl, 2008).
In addition to their practical uses, Tilia are valued as city trees.
Besides their aesthetic appeal, they are also surprisingly resistant to pollution and drought. As such, Tilia trees readily grow in urban environments (Pigott, 2012). While common in European urban areas (Andrianjara et al., 2021;Rahman et al., 2017;Wolff et al., 2019), Tilia trees are less often seen in Asian cities.
Three endemic species of Tilia are native to the Japanese islands.
Tilia japonica (Miq.) Simonk. (シナノキ or アカシナ) is the most widespread and can be found in all of Japan other than the Ryukyu Islands.  Kurata & Hamaya, 1968-1976 inouei Hatus.-ブンゴボダイジュ) can also be found in southern Japan; it is unclear whether T. mandshurica is a native or introduced species in Japan (Pigott, 2012). Tilia miqueliana Maxim. (ボダイジュ) was brought to Japan over 1000 years ago by monks from China and Korea during the establishment of Buddhism in the island country (Macomber, 2022;Pigott, 2012). In recent times, other Tilia species (e.g., T. cordata Mill. or T. × europaea L.) are also planted in Japanese urban environments, parks, and roads (Tanda & Nishiuchi, 2000;Tokyo Chuo City Tourism Association, 2020 Kurata andHamaya (1968-1976).
Despite the recognized economic and cultural (Forestry Agency Japan, 2012;Miyake, 2004) and suggested ecological (Janowski & Nara, 2021) importance of Tilia trees in Japan, they are rarely studied, and only limited information about them is available (Table 1).
The primary purpose of this review is to outline the value Japanese Tilia trees have to people and to present this information in an organized way. Following the categorization of values trees provide to people suggested by Rivers et al. (2022), the importance of Tilia trees in Japan was divided into three categories: cultural and aesthetic, economic and livelihood, and ecological. Raising the awareness of trees' relevance may increase the scientific attention they receive. Moreover, summarizing this information in one place could help highlight the gaps in our current knowledge of Japanese Tilia trees and the Tilia genus in general.

| Religious and symbolic significance
Tilia trees are important in the Japanese Buddhist tradition.
According to the Buddhist teachings, the Buddha, Siddhartha Gautama, attained enlightenment by meditating under a Ficus religiosa tree (Gethin, 1998), referred to as pútíshù (菩提树) in Chinese and bodaiju (菩提樹) in Japanese. Ficus religiosa, native to the Indian subcontinent, was characteristically depicted in early Buddhist iconography as having heart-shaped leaves. As the religion spread throughout regions of China where F. religiosa did not grow naturally, it was replaced with other tree species similar to the iconographic depictions, for example, Ginkgo biloba, Syringa reticulata, or T. miqueliana (Wang et al., 2020). After Buddhism was brought to Japan, this last tree species was also imported and planted on temple grounds as the holy bodaiju tree during the 12th century (Macomber, 2022;Pigott, 2012). Today still, T. miqueliana can be found growing in many Buddhist temples in Japan ( Figure 2), even after F. religiosa trees were also brought to Japan in the 19th century (Kimura, 1958). Interestingly, while T. miqueliana was also often used for Buddhist sculptures in China and Korea (Choi et al., 2022;Tazuru et al., 2022), it was rarely used for this purpose in Japan. One of the few Japanese Buddhist sculptures known to be made of Tilia wood is the Amida-nyorai in the Tenpourinji temple in Kobe (Kohara, 1964).
Other Tilia species were also sometimes used in the Buddhist context in Japan. Tilia mandshurica was often planted as bodaiju on temple grounds in southern Japan, being brought from the nearby Korean peninsula (Pigott, 2012). Similarly, native T. japonica and T. maximowicziana were planted in temples in northern Japan (Miya, 2016). The leaves of Japanese-native T. japonica with religious inscriptions written on them were found inside a Buddha sculpture in Bujoji temple in Kyoto (Seya, 2000). Several Tilia trees recognized as important by local Buddhist communities can be found across Japan.
Some Tilia trees in Japan are considered shinboku (神木), holy trees in Shinto. Shinto is a native Japanese religion that emphasizes nature worship (Bowker, 2002). According to its beliefs, some objects or places may become yorishiro (依代)-representatives, in which spirits can enter to interact with people (Okada, n.d.).
Shinboku are yorishiro trees, commonly of impressive age and size.
The most well-known Tilia shinboku is an over 800 years old T. japonica in Kumanokotai Shrine in the Nagano prefecture (Kumano-Kotai-Jinja, n.d.; Town of Karuizawa, 2016). While T. japonica is the most common Tilia species to be recognized as shinboku (Miya, 2016), as 科野國) already in the 8th century when it appeared in Kojiki, the earliest known Japanese literary record (Suzuki, 1935). According to Ichikawa (1994), Shinanokuni (as well as many villages therein using the character 科 in their names) was named after T. japonica (shinanoki; 科の木). Common in the region, the tree was economically important at the time; its bast was used to weave fabrics and ropes.

| Recreational spaces
Despite their cultural significance, Tilia trees are less common in cities and parks in Japan than in other parts of the world. A major exception to that is the city of Nagano, where T. japonica, a designated city symbol, is often seen in parks and on roadsides (Nagano were first brought to Japan as ornamental trees (Higo, 1961

| Honey production
Tilia trees are important honey plants in Hokkaido and northern Honshu, the primary bee-keeping regions in Japan (Masaka, 2016;Masaka et al., 2013;Okada, 1981;Taniguchi et al., 2012). In 2021, to Japan in the 19th century (Higo, 1961). Tilia spp. and R. pseudoacacia each contribute roughly one-third of Hokkaido honey production (Masaka et al., 2013). However, the efficiency of honey production from Tilia spp. exceeds that of other honey plants in Japan, with monofloral Tilia honey achieving higher yields per hive per year (Masaka & Sato, 2011;Okada, 1981). The number of Tilia trees in an area was shown to correlate exponentially to the proportion of beehives producing monofloral Tilia honey in that area (Masaka et al., 2013). This suggests that if Tilia flowers are available, honeybees in Japan prefer them over other honey plant species. The most significant disadvantage of Tilia spp. to Japanese beekeepers, and one of the reasons for introducing R. pseudoacacia, is the unpredictability in nectar output year to year that characterizes Tilia. Nearly every other year, Tilia trees produce less than half the regular amount of nectar, and their flowers are also comparatively more vulnerable to weather (Masaka, 2016;Okada, 1981).
Similar to western Tilia spp. monofloral honeys (Juan-Borrás et al., 2014), Japanese Tilia honey is characterized by a strong herbal smell and bright yellow color (Okada, 1981). Flavor-wise, it is sweeter and less sour than most other Japanese honeys (Mayama et al., 1982).

While the information on the composition and health benefits of
Japanese Tilia honey is limited, more is known about Tilia honeys in general. They have a high mineral content (Bodó et al., 2021;Juan-Borrás et al., 2014;Oroian et al., 2015). Although the antioxidant properties of Tilia honeys are average compared with other monofloral honeys, they much exceed the more commercially popular R. pseudoacacia honey (Bodó et al., 2021). Tilia honeys have one of the strongest antibacterial properties (Balázs et al., 2021). Due to their calming properties, Tilia honeys are also used to alleviate insomnia and stress (Yaniv & Rudich, 1997). leaves and flowers is also acknowledged in Japanese sources (Shoyama, 2014

| Wood
While Tilia wood (basswood) has an exceptionally low density and is soft for hardwood (Brush, 1922), T. japonica has relatively high wood density among the Tilia species. With an average density of around 450 kg/m 3 (Fukazawa & Ohtani, 1979), its wood is denser than T. americana (around 380 kg/m 3 ; Brush, 1922) and is comparable with the European T. cordata (410-500 kg/m 3 ; Dünisch, 2017).
Japanese basswood is traditionally used for cabinets, wooden boxes, small, light items (e.g., chopsticks and pencils), or kyougi (経木)-thin layers of wood used as a substitute for paper and for packaging. It is also an important wood used for plywood and veneers (Japan Wood Products Information & Research Center, n.d.;Yahagi, 2018).
Plywood and veneers made with T. japonica wood are of higher quality and better adhere compared with those made with Chinese Tilia species (Kishino & Nakano, 2003). Due to its softness, in Hokkaido T. japonica wood is often used to carve commemorative bear sculptures (Shibuya et al., 2019).

| Bast
Tilia spp. used to be an important fiber crop in Japan, and its bast fibers used by both the Japanese people and the Ainu people of Hokkaido. Peeling the bark of Tilia spp. is easier and can be done for longer periods each year (until mid-July) compared with other tree species (e.g., Ulmus laciniata and Ulmus davidiana var. japonica) that were used for bast in Japan (Sato, 2018). The Ainu people utilized bast of T. japonica and T. maximowicziana, the latter being less popular for its lower quality (Saito, 1995). They used Tilia bast for various purposes, for example manufacturing clothes, carrying bags, floor mats, ropes, and fishing nets (Hitchcock, 1892;Saito, 1995).
Attus, the Ainu fabric used for clothing resembling Japanese kimono, was typically weaved either from U. laciniata or T. japonica bast (Sato, 2018).
The ethnic Japanese people used to weave T. japonica bast cloth called shinafu (シナ布), a smooth, elegant fabric resistant to wrinkling (Tamaki, 1971;Yamanaka et al., 2003). Manufactured in different forms since the Jomon period (14000-300 BCE), shinafu is one of the oldest types of fabric continually produced and used in Japan (Yamanaka et al., 2003). Shinafu was not the only Tilia material used by the Japanese people to make clothing. Due to their waterproof properties, wide straps of bast were bound together to make raincapes used by farmers (Pigott, 2012). Other than for clothes, the Japanese used T. japonica bast fabric to produce straining cloths traditionally used in alcohol production. In northern Honshu, T. maximowicziana bast cloth was used for traditional bags for soy sauce fermentation (Yanagita, 1941). On the island of Kyushu, T. kiusiana and T. mandshurica var. rufovillosa were primarily used instead of T. japonica. Tilia mandshurica var. rufovillosa was particularly preferred by the local people who often planted it close to their rice fields to easily collect the bark (Pigott, 2012;Yanagita, 1941).
In response to the post-war economic growth, many people in Japan pursued office jobs at the cost of traditional occupations.
This has led to the number of people producing Tilia bast fabrics drastically decreasing, resulting in a decrease in the fabric's availability and an increase in its price (Tamaki, 1971).  (Pigott, 2012).
Although some studies of pollination in Japanese Tilia spp. are available, they focus on flower physiology and provide only limited information on the visiting pollinators (Ito & Kikuzawa, 1999, 2000, 2003. The pollination ecology of Japanese Tilia spp., especially in southern Japan, is largely underexplored. Insects reported to visit Tilia flowers in Japan are summarized in Table 2. Studies of Bombus spp. in northern Japan identified T. japonica and T. maximowicziana as crucial sources of nectar for these ecologically and economically essential pollinators (Inari et al., 2012). Tilia
Planting Tilia trees in cities may potentially lead to an increased diversity of soil fungi (Csizmár et al., 2021;Janowski & Leski, 2022), indirectly improving the soil condition. Several studies indicated that Tilia spp. readily associate with the Tuber genus, with some suggesting that Tilia trees could be considered for use in truffle orchards (Rudawska et al., 2019;Timonen & Kauppinen, 2008).
As the majority of Tilia ectomycorrhizal relation studies are conducted in Europe, the ectomycorrhizal relations of Japanese Tilia spp. are not well known. A single study of ectomycorrhizal communities hosted by T. japonica in Japanese forests revealed a high diversity of fungal partners, many of which were previously unreported or species first recorded in Japan (Janowski & Nara, 2021). Janowski and Nara (2021) suggest that T. japonica might be playing a significant role in the local ectomycorrhizal networks, increasing their connectance and stability.

ACK N OWLED G M ENTS
I want to warmly thank Hosana Janowska for help in translating the Japanese resources using older language, and the general support during writing.

DATA AVA I L A B I L I T Y S TAT E M E N T
No new data was created in this study.